Herpesviruses replicate and package their genomes in the cell nucleus. In order to begin its process of escape from the cell, the virus must pass through the nuclear membrane by first budding into the inner nuclear membrane in a process called primary envelopment. The mechanism of herpesvirus envelopment is significant to human health from two points of view. First, this process represents an attractive target for therapy in that it is dissimilar in many ways to any normal cellular process, essential to the virus, and common to all herpesviruses. Second, the envelopment machinery alters the organization of the nuclear envelope and provides a useful tool for studying that organization. The research proposed here builds on our studies of herpes simplex virus UL34, an essential component of the envelopment apparatus. Results from our initial period of funding suggest that this protein plays critical roles in at least three aspects of envelopment including (i) recruitment of viral proteins to the nuclear envelope, (ii) dispersal of nuclear envelope components that prevent access of the capsid to the nuclear membrane, and (iii) wrapping of the nucleocapsid in the nuclear membrane. The specific goals of the proposed research are threefold 1. We will define essential functions of the UL34 protein by characterizing a set of seven non-functional mutant UL34 proteins already in hand, and others that we will generate by mutagenesis of conserved residues, for their ability to perform various functions required for envelopment. 2. We will characterize critical interactions between the UL34 protein and other viral proteins involved in envelopment. This will include experiments to test the hypothesis that UL34 mediates membrane wrapping of the capsid, and a screen for interactions of UL34 with other viral proteins that may participate in envelopment. 3. We will fully characterize changes in the host cell nuclear lamina associated with infection and determine the mechanism by which UL34 and other viral proteins accomplish those changes.